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Generation of compressional Alfvénic rogue and solitary waves in magnetohydrodynamic plasmas is investigated. Dispersive effect caused by non-ideal electron inertia currents perpendicular to the ambient magnetic field can balance the nonlinear steepening of waves leading to the formation of a soliton. The reductive perturbation method is used to obtain a Korteweg-de Vries (KdV) equation describing the evolution of the solitary wave. The height of a soliton is proportional to the soliton speed 'U' and inversely proportional to plasma 'β' (ratio of plasma thermal pressure to pressure of the confining magnetic field) and the width of soliton is proportional to the electron inertial length. KdV equation is used to study the nonlinear evolution of modulationally unstable compressional Alfvénic wavepackets via the nonlinear Schrödinger equation. The characteristics of rogue wave influenced by plasma 'β' and the electron inertial length are described. [ABSTRACT FROM AUTHOR]

Coulombic expansion of an atomic cluster can significantly affect the growth of stimulated Raman backscattering in cluster embedded plasmas. The pulse attenuation and the collisional absorption occur during the early phase of cluster expansion, competing against each other in determining the Raman threshold intensity in a cluster plasma. The threshold laser intensities estimated for various wave numbers of the electron plasma waves are found to be consistent with the previous result [P. K. Tiwari et al., Phys. Plasmas 14, 103101 (2007)]: Collisional threshold intensities are to be of 1∼105 W/cm2 at the electron-ion collisional frequency ≈1013 s-1, and the pulse attenuated threshold intensities are to be of ∼1013 W/cm2 for short pulse length ∼20 fs. The pulse attenuation and collisional absorption of Raman threshold intensities are found to be inversely proportional to both the pulse duration and attenuation length. [ABSTRACT FROM AUTHOR]

The equations of resistive magnetohydrodynamics (MHD) are recast in a form that is useful for studying the evolution of those toroidal systems where the fast magnetosonic wave plays no important role. The equations are exact and have ∇ · B=0 satisfied explicitly. From this set of equations it is a simple matter to derive the equations of reduced MHD to any order in the inverse aspect ratio ε of the torus and for β∼ε or smaller. This is demonstrated by deriving a reduced set of MHD equations that are correct to fifth order in ε. These equations contain the exact equilibrium relation and, as such, can be used to find three-dimensional stellarator equilibria. In addition, if a subsidiary ordering in η, the resistivity, is made, the equations of Glasser, Greene, and Johnson [Phys. Fluids 8, 875 (1967); 19, 567 (1967)] are recovered. This set of reduced equations has been coded by extending the initial value code hilo [Phys. Fluids 26, 3066 (1983)]. Results obtained for both ideal and resistive linear stability from the reduced equations are compared with those obtained by solving the full set of MHD equations in a cylinder. Good agreement is shown for both zero and finite-beta calculations. Comparisons are also made with analytic theory illuminating the present limitations of the latter. [ABSTRACT FROM AUTHOR]

Abstract: The Korea Superconducting Tokamak Advanced Research (KSTAR) device aims to demonstrating the steady-state operation of high-performance advanced tokamak (AT) modes. In order to meet this research goal it is critical to have a good magnetohydrodynamic (MHD) stability, so that KSTAR adopted a strong plasma shape and a conducting wall close to plasma for such stability. An early calculation during the KSTAR design phase had shown that a target AT mode stable up to above 5 can be then obtained. A recent work by Katsuro-Hopkins et al. [O. Katsuro-Hopkins, S.A. Sabbagh, J.M. Bialek, H.K. Park, J.G. Bak, J. Chung, et al., Equilibrium and global MHD stability study of KSTAR high beta plasmas under passive and active mode control, Nucl. Fusion 50(2010) 025019] showed, however, that the maximum value can be substantially lower than 5, unlike the earlier result. In this work, we present a more detailed study on the MHD stability limit of the KSTAR target AT mode and try to clarify the discrepancy observed in the previous two works. It is shown that in the reverse-shear plasma the target mode with above 5 can be obtained if the pressure profile is relatively peaked, but the maximum value is substantially reduced below 5 if the pressure profile becomes broader. This result suggests the importance of a proper control of the pressure profile to get the high-beta AT mode in KSTAR. [ABSTRACT FROM AUTHOR]